Knee pain is remarkably prevalent, with pain on most days of a month affecting roughly 25% of adults age 55 and over. In most studies, half of the persons with frequent knee pain do not have x-ray OA. Knee pain is a major cause of disability, even in persons without symptomatic osteoarthritis (Guccione et al, 1990). In fact, there is a higher risk of mobility disability in those with knee pain who do not have x-ray OA than among those with x-ray OA who have no pain (Guccione et al, 1990). We have shown that certain MRI features are correlated with the presence of knee pain in knees with osteoarthritis. These findings emanated from studies of those with knee OA, and multiple coexistent structural changes exist in these knees, making it hard to isolate the likely source of pain. Also, knees with pain almost all have synovial proliferation on MRI, but it is unclear how extensive this synovial proliferation is and whether it also occurs frequently in nonpainful knees. Of all persons with knee pain in the community, we do not know how many have periarticular vs. intraarticular pathology and which articular pathologies are most likely associated with pain. Using data being collected in the MOST Study, a longitudinal study of persons from the community with knee pain at high risk of developing OA or with preexisting symptomatic OA, we will address a series of questions about the structural correlates of knee pain: 1.How many persons in the community with knee pain have pain emanating from the knee joint? 2. Using gadolinium injections to allow comprehensive assessment of synovial proliferation and focusing on knees with pain but little x-ray OA, what are the structural findings most likely to be associated with intraarticular knee pain? 3. Is the volume of synovium in the knee associated with the severity of knee pain? 4. Are there specific MRI findings associated with pain at rest? and 5. Following subjects over time, can we identify sources of pain by identifying whether the development or resolution of knee pain corresponds with development or resolution of a structural lesion? Addressing these questions will help us better understand the sources of knee pain and will therefore aid in its prevention and treatment. [unreadable] [unreadable] [unreadable]